Browsing by Author "Kilpi, Oskari"

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    Catalytic pulp bleaching
    (2016-05-08) Kilpi, Oskari; Chenna, Naveen; Kemiantekniikan korkeakoulu; Hiltunen, Eero
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    Reduction of sulfate emissions in bleached softwood kraft pulp mill
    (2019-05-07) Kilpi, Oskari; Pekkanen, Lauri; Tikkanen, Antti; Kemian tekniikan korkeakoulu; Dahl, Olli
    The aim of this thesis was to examine where the pulp mill sulfate emissions are formed and ways to reduce them. Sulfate emissions increase the water salinity and may increase eutrophication. Sulfate emissions of pulp mill are mainly caused by recovery boiler fly ash purging and the use of sulfuric acid in pH adjustment. Especially softwood pulp mills have excess sulfur in sodium and sulfur balance, since tall oil production requires sulfuric acid. The conventional way to reduce the excess sulfur is to purge part of recovery boiler fly ash, which includes sodium sulfate. In the experimental study, several process variables for the reduction of sulfate emissions were calculated. These variables were the replacement of sulfuric acid by hydrochloric acid in pH adjustment, integrated chlorine dioxide plant, carbon dioxide semi acidulation of tall oil, replacement of aluminum sulfate by polyaluminum chloride in water treatment, fly ash treatment and internal sulfuric acid production from non-condensable gases. The effect of liquor heat treatment and green liquor stripping and carbonation was calculated for the capacity increase of sulfuric acid plant. Five cases were composed based on the calculated process variables, which represented a feasible pulp mill main dimensioning balances. These cases were; Case 1: only chemical replacements, Case 2: sulfuric acid plant, Case 3: integrated chlorine dioxide plant, Case 4: integrated chlorine dioxide plant and sulfuric acid plant and Case 5: integrated chlorine dioxide plant and sulfuric acid plant with lignin separation and green liquor stripping and carbonation. It was concluded that sulfate emissions were reduced, when sulfur input decreased, the sulfur cycle was more closed or sulfur-containing chemicals were replaced by other chemicals. The reduction of sulfate emissions reduced also the make-up chemical consumption. Cases 4 and 5 had the lowest sulfate emissions. Case 2 had the lowest make-up chemical consumption.